The data in the below record the service time (in minutes) required to service disk drives from three different manufacturers by three different technicians. Each technician was randomly assigned to repair five disk drives for each brand of disk drive. (a) Compute the estimated cell means and display your results in the format. (b) Plot the estimated cell means (i, yij.)(i = 1,…, 3) for each brand in the format. Does the graph support or refute the assumption that there are no interactions between the technicians and the brand of the disk drive? (c) Test for the existence of interactions and main effects by computing the two-way ANOVA .
(d) Compute a 95% confidence interval for the time to service each brand of drive. (e) Compute a 95% confidence interval for the time for each technician to service a drive.
(Source: Neter, Wasserman, and Kutner (1990), Applied Linear Statistical Models, p. 723, R. D. Irwin, Homewood, IL. Used with permission.)